# Expression of Transposable Elements throughout the Fasciola hepatica Trematode Life Cycle

## TL;DR

This study explores how transposable elements, once seen as genomic parasites, may regulate the life cycle of the liver fluke Fasciola hepatica.

## Contribution

The study reveals stage-specific transposable element expression patterns and their potential regulatory roles in trematode life cycle transitions.

## Key findings

- Transposable element transcription peaks during egg and metacercariae stages of Fasciola hepatica.
- Some transposable elements show homology with long non-coding RNAs and have potential transcription factor binding sites.
- Transposable element activity is highest in early life stages, suggesting roles in developmental regulation.

## Abstract

Background: Transposable elements (TEs) are major components of eukaryotic genomes. The extensive body of evidence suggests that although they were once considered “genomic parasites”, transposons and their transcripts perform specific functions, such as regulation of early embryo development. Understanding the role of TEs in such parasites as trematodes is becoming critically important. Fasciola hepatica, a parasite affecting humans and livestock, undergoes a complex life cycle in diverse environments and hosts, and knowledge about its life cycle regulation is scarce so far. Methods: We summarized the data regarding the repetitive elements in F. hepatica and conducted bulk RNA-seq analysis across its life cycle stages. TE expression profiles were analyzed, focusing on differential expression and potential homology with previously described long non-coding RNAs (lncRNAs). Results: Differential expression analysis revealed stage-specific TE transcription patterns, notably peaking during egg and metacercariae stages. Some TEs showed homology with known lncRNAs and contained putative transcription factor binding sites. Interestingly, TE transcription levels were highest in eggs and metacercariae compared to adults, suggesting regulatory roles in trematode life cycle transitions. Conclusions: These findings suggest that TEs may play roles in regulating trematode life cycle transitions. Moreover, TE homology with lncRNAs underscores their significance in gene regulation.